Work-centering device for machine tools



Das. 26, 1922.

A. TURNER ET AL WORK CENTERING DEVI cs PoR MAemNE Toons.

. f zo Albev mmm Hom/mrd W. Umbav Fr LED SEP-r. 22. 1g

Patented 26,

Application tiled September To all who/m t may concerny Be it known that we, ALBERT TURNER and l-lowAizn W. DUNBAR, citizens oi the United States of America, residing at Worcester,

in the county of l/Vorcester and State ot Massachusetts, have invented. certain new and useful lmprovements in lWork-(Centering Devices for Machine Tools, et which the following is a Jiull, clear, and exact speciliio cation.

Our invention relates to work-centering devices for machine tools, such as grinding machines or lathes, and more particularly to an attachment for convert-ing; a fined or l5 dead center into a running,` or live center.

In grinding' operations the work usually supported between centers held against rotation, commonly termed dead centers, ar-

ranged on the head and toot stoclrs oit the machine, one oit said centers being longitu dinally movable to allow of placing` the work into position. Suitable (logging means are clamped to the work and the work is rotated by engagement oi the dog with a driver on the head stock. ln some work, however, such as the grinding oi? twist drills, since the work is not adapted to be supported on the usual lined centers, it becomes necessary to 3G provide a special runnii'ig` center construei tion on the headstock to engage and drive the work. lt has been proposed to use a special running' center and driver on a lined center 'for this purpose, but the devices heretofore constructed have been open to the obiection that, since no adequate provision has been made to take up the wear due to side thrust caused by the action of the tool on the work, after short time side play ene0 sues with consequent marrin; of the work. lt is an object et our invention to overcome these ditliculties by .mounting a running center attachment on a 'lined center in such a way that the wear is automatically talren up and the running center held side play at all times by the thrust exerted thereon by the work, whereby it will always run true, regardless of the wear, and thus produce work oi" a uniform duality. se Vtfith this and other objects in view, as

per.

i, 9243. Serial No. 2,683

will appear trom the Yfollowing` disclosure, our invention resides in the combination of parts set forth in the specification and covered by the claims appended thereto.

terence being had to the accompanying drawings in which like numerals indicate like parts:

TFigure l is sectional view showing our running` center attachment mounted in place on the headstock ot a grinding machine;

Fig. 2 is a iront elevation thereof showing the driver pin but omitting the other parts oi the headstock shown in Fig. l;

3 is a `fragmentary ectional view of a modified centering means adapted for work having a center hole; and

Fig. 1l is a side elevation of another form of centering and work drivingv means which may be used in connection with our invention.

la the practice orp our invention, we provide a running center attachment for use on the headstoclr orp a machine tool to hold the 1 rllhe centering device is preferworn true. ably mounted on spaced bearings, one of which takes both the end and side thrusts of the work, and, in our preferred arrangement, this latter bearing is tapered and arranged adjacent the work-engaging part of the attachment. rl`his attarhment is ro- 8O tated by a suitable driver on the rotatable tace plate which may be, and preferably is, the same driver as that which rotates the work when the latter is supported on iXed centers. llfhere desirable to use a running center on the tail/steelt, our attachment can obviously7 be used there as well as on the headstoclr.

ln the lspecific embodiment of our invention selected :tor illustration we have shown our improved centering; device as applied to a headstoclr et a usual construction provided with a spindle l having` a central opening 2 into which the tapered shank 3 of the lined center 4 is driven. The usual 95 'tace plate' 5, we have shown connected by suitable means, such as the screws 7, with a gear 6, this gear being mounted for rotation through its wide bearing hub 8 and a bearing bushing 9 on the i/tporward end. of the 1,00

spindle l. The means for retaining the gear and bushing in place on the spindle may consist oit an annular plate l0 connected to the spindle as by screws ll. The connected gear and tace plate may be' driven trom` the usual shaft carrying a cone pulley arranged on the headstock. The face plate 5 carries the usual driver pin 13 adjnstably mounted in radially extending T-sl0ts lfl thereon.

i ln carrying out our invention We preterably substitute for the usual fixed center a center e having a flange l5 thereon, intermediate its ends, but We may leave the usual center in place and mount our running`- center attachment thereon, it desired. From the flange l5 forward; rthe center has the usual cylindrical form lWhich terminates in a conical point 16. On this forward portion, We mount our running center attachment l? which may be provided with ,a dial iiange 18 having a slot 19 to receive the driver pin i3. This flanged construction insures a balanced device Well adaptedl for connecting the attachment to thel driver pin 13.

'The attachment consists essentially of a hollow body portion 2O` rotatably supported 0n thecenter et by means of spaced bearings 2l and 22A and provided with Asome term of {voiler-entering means- 23', andl il.i used: on: the headstoclr as shown, with Aa iwrlz-driving means such as the dogsf. ll'c have shown the body 20 of the attachment as bei-ng oi generally conical shape and formed' xiv-ith aligned cylindrical bores 25, 26 and 2!v of increasing diameter from the front-- of the attachment to the back and forming the rear wardly 'facing shoulders 28'and 29. lThe forward bore 25- is relatively short'and' receives the tightly fitting bearing bushing 30 of hard metalsuch as hardened steel. This bushing is provided at its rearward" end with a conical opening to receive the conical point lo of the center pin and thus forms a combined radial and end thrust bearlng adapted to take up or Wear and maintain the Work accurately centered at all times.l rlhis bushing 30-has formedon its rearward end an outwardly extending flange 8l which engages the sholillder 27S to prevent forward movement of the bushing under the end thrustb The centering means is shown (Fic: l) in the fornaci? a conical depression formed in the bushing 3Q to `receivewcrlr having a mating slr,pecl-enda such a twist ill; but it is obviousthat thismaytalre on a variety of forms, depending upon the nature of the work being'operated onf in l* l wehave shoivn a modified `form in which the centering means 28 on thev bushing 30" is in the form of a conical point, such as s usually employed in` connection withv Worlfhaving'la cfefrjter!hole(Y Thegbody 2O ot the -attaclinientfis shown;j somewhat, lQCliied in thisl ligure, but-th principle of? Lafraise operation is the same. The bushing 30' is driven into the bore 25 corresponding` to the bore in Fig. l and a 'flange 3l on the bushing bears against the shoulder 2S on the bod-y ot the attachment.

ln Fig. et We have shown a still further modification of the bushing which We may employ. rllhe bushingk 30 shown in this ligurefhas a centering means 23 inthe torni of a pyramid. This termV is especially adapted 'for centering and drying small Work having centerv holes of mating ilorm, thus avoiding' the use of separate Work-driving means such as the dog 2e shown in Fig. l. V

vrllhe central bore 2,6 is oit, a diameter someufhat larger` than the center et to avoid lirictional lengagement therewith. To 'turther minimize friction the bearing 22 maybe aball bearing as shown, consisting oli' the in-r ner and outer ballraceways 32Vand 33 yand the balls `Whenthe parts are in place the inner raceivay' 32 lits tightly onto the cylindrical: portion ot the center and bears against the flange l5 thereon. This bearing is housed inthe enlarged bore 2? of the attachment, the rear-end' of which is prefer-` ably closed to exclude dust andy dirt from the bearing by an annular plato 35 suitably connected as by screws 3G to the rear side of the attaclnnent. rlhis plate also serves to holdtlie ballv bearingfinl place in body 20. To allow endwise movement 'of the attachment to automatically take up for Wear in the conical bearing 2l', we provide a close. sliding it betweeny t-he outer ball racewayf 33 andthe Wall ot' the bore 27T,y and a clearance space 37 lbetween the shoulder 29 and the.

ball bearing raceways.

It Willbe apparent 'from this construction, sincev the Work is always held against the center by a certain pressure which, especially` inl the case oit relatively smallv work, is usually exertedV on the tailstocli spindle by a spring, that any Wear in the conical bearing 2l Will beV automatically takenY up, thus avoiding all side play, which would have a tendency to injure the Werk. It should also be noted' that the Work-engaging part 28' is located at a comparatively short distance trom the bearing 2l, seth-at, even if the rear hallbearing shouldv7 in l the eiii'ect cn the ivcfliA would be almost neg ngi-blea Having thusdescrihed` ou We claim as new anc) desire ters `Patent is:

l. A ivorlccentering and dri-ving device for machinetools, comprising a fixed' center, a running center attachment rotatably mounted. thereon, a work driver on said attachment and spaced radial bearings -between said fixed center andA said attachment, one of said"floearingsl compris-ing cooperating tapered-f surfaces onl said center and attach 1,440, ree

ment to taire the end thrust and avoid side play between the fixed center and the running center attachment.

2. A work-centering and driving device 'for machine tools, comprising a fixed center, a running center attachment rotatably mounted thereon and having a work-engaging part, and spaced radial bearingsbetween said center and said attachment, one of said bearings comprising cooperating conical surfaces on said center and attachment adjacent the work-engaging part on the latter to take the end thrust and avoid side playvbetween the fixed center and the running center attachment.

if* work -holding center' for machine tools, comprising a fixed center, a rotatable centering means having a. work-holding part mounted on said fixed center, and spaced bearings for said means, one oit said bearings comprising a tapered bearing adjacent said work-holding part to take radial and end 'thrusts and the other comprising a radial bearing allowing endwise movement of said centering means to take up the wear in the tapered bearing.

Il. A centering device for the headstock oit machine tools, comprising a fixed center, a

running .center attachniient rotatabljT mounted thereon, and spaced bearings for said attachment, one o' said bearings comprising cooperating tapered bearing surfaces .between the end of said center and said attachment and the other of said bearings comprising an anti-friction bearing allowing endwise movement or the attachment to take up the wear in the tapered bearing.

5. A cen ering device for the headstock or machine tools, comprising` a fixed center, a rotatable centering attachment having a work-holding and driving means mounted thereon, spaced bearings for said attachment, one of said bearings comprising a tapered bearing adjacent said work-holding means to taire both radial and end thrusts, the other comprising a radial ball bearing` arranged so as to allow endwise movement between said bearing and the rotatable attachment to take up for wear in the tapered hearing, and means for driving the rotatable attachment.

Signed at Worcester, Massachusetts, this th day of Sept., 1920.

ALBERT TURNER. HONARD WESLEY ,DUNBARa 

